The present invention relates to a liquid crystal display device which displays visible information, such as numbers or characters, using liquid crystal filled between a pair of substrates. The present invention also relates to an electronic device employing such a liquid crystal display device as a visible image display portion.
In recent years, liquid crystal display devices have been widely used as a visible image display portion of various electronic devices, such as portable telephones and portable information terminals. A known type of conventional liquid crystal device comprises a liquid crystal structure consisting of a pair of substrates with liquid crystal filled therebetween, and an illuminator for illuminating the liquid crystal structure with light. Another known type of conventional liquid crystal device is the so-called transreflective liquid crystal display device which is capable of reflecting and transmitting light.
The transreflective liquid crystal display device comprises a semitransmissive type light reflecting plate at the back side of the aforementioned liquid crystal structure and an illuminator, which are disposed successively. When the transreflector liquid crystal display device is used in places which get a lot of outside light, such as outdoors, it is used as a reflective liquid crystal display device, since the illuminator is not used. When the transreflective liquid crystal display device is used in places which get only a small amount of outside light, it is used as a transmissive liquid crystal display device, since the illuminator device is used and turned on. Such a transreflector liquid crystal display device is disclosed in, for example, Japanese Unexamined Patent Publication No. 57-049271.
Compared to the so-called reflective liquid crystal display device which displays information by disposing only a light reflecting plate at the back side of the liquid crystal structure and using only outside light, the transreflective liquid crystal display device has the problem that the display becomes dark when information is displayed by reflection. This is because in such a transflective liquid crystal display device light transmission is achieved by making the reflective layer, such as an Al (aluminum) layer, of the light reflecting plate thin, or forming an opening, for allowing light transmission, in the reflecting layer, so that the brightness of the display obtained by reflection is sacrificed.
In addition, since in the conventional transreflector liquid crystal display device the illuminator that is disposed at the back side of the liquid crystal structure illuminates the liquid crystal structure through a semitransmissive reflecting plate, a very bright light source is required to illuminate the liquid crystal structure brightly, resulting in large electrical power consumption.
To overcome this problem, the applicant, in Japanese Unexamined Patent Publication No. 6-324331, has disclosed a so-called front light type liquid crystal display device that has an illuminator disposed at the observer side of the liquid crystal structure. For example, as shown in FIG. 14, the front light type liquid crystal display device includes an illuminator 7 disposed at the observer side (the top side in FIG. 14) of the liquid crystal structure 6 consisting of a pair of substrates with liquid crystal filled therebetween; and a light reflecting plate 8 that is disposed at the side opposite to the observer side of the liquid crystal structure 6. The illuminator 7 includes, for example, a light source 2, a transmissive light-guiding member 3 with protrusions 4a, and a side face reflecting plate 10. As shown in FIG. 13, the protrusions 4a are disposed in a regular or irregular dot arrangement on a surface of the light-guiding member 3.
This liquid crystal display device is used as a reflective liquid crystal display device when it is used in places which get a lot of outside light, such as outdoors, and as a transmissive liquid crystal display device when it is used in places which get only a small amount of outside light. In the former case, information is displayed by transmission of outside light through the transmissive light-guiding member 3, and in the latter case, information is displayed by using illuminating light of the light source 2. When the liquid crystal display device is used as a reflective liquid crystal display device, light beams from the light source 2 take the paths indicated by S1 and S2 of FIG. 14, so that they propagate through the light-guiding member 3 as they undergo total reflection, and arrive at side faces of corresponding protrusions 4a, after which they leave the light-guiding member 3 and illuminate the liquid crystal structure 6. When such a front light type illuminator 7 is used, a semitransmissive light reflecting plate is not required, thereby allowing a bright display to be provided by light reflection.
However, the conventional liquid crystal display device of FIG. 14 allows dust to easily enter between the liquid crystal structure 6 and the light-guiding member 7. When dust enters between them, light from the light source 2 that has been turned on is scattered around the dust, causing the dust to become visible to the observer.
In the conventional liquid crystal display device, the surfaces of the liquid crystal structure 6 and the light-guiding member 3 are in direct contact with each other. In this case, there are particularly no problems if the distances between portions of the liquid crystal structure 6 and portions of the light-guiding member 3 are equal throughout the entire region of surface contact. However, when distances vary, interference patterns or the so-called newton rings are produced, making the visible image displayed on the liquid crystal display device difficult to see.
In view of the above-described problems, it is an object of the present invention to make it possible to prevent the quality of a visible image to be displayed from being reduced as a result of entry of dust into the liquid crystal display device and as a result of non-uniform close contact between the light-guiding member and another member of the liquid crystal display device.
To these ends, according to the present invention, the liquid crystal device may have the following structures.
(1) A first liquid crystal display device of the present invention comprises a liquid crystal structure having liquid crystal filled between a pair of substrates, a light source which emits light, and a light-guiding member, disposed at the observer side of the liquid crystal structure, for guiding the light from the light source to the liquid crystal structure, wherein a spacer member is disposed between the light-guiding member and the liquid crystal structure at the peripheral portions of the light-guiding member and the liquid crystal structure so as to be in close contact with the light-guiding member and the liquid crystal structure.
In the liquid crystal display device having the above-described structure, light from the light source strikes a light-guiding member and propagates therethrough, after which it leaves the light-guiding member and illuminates a liquid crystal structure. By controlling the voltage applied to a pair of electrodes in the liquid crystal structure, the light transmission state of the light is varied, so that a visible image, such as a number or a character, is displayed as a result of contrast, resulting from varying the light transmission state.
In addition, in the liquid crystal display device, a spacer member is disposed between the light-guiding member and the liquid crystal structure at the peripheral portions thereof so as to be in close contact therewith, so that dust no longer enters between the light-guiding member and the liquid crystal structure, as a result of which the quality of a visible image to be displayed on the liquid crystal display device can be maintained at a high level over a long period of time. The spacer member also keeps the light-guiding member and the liquid crystal structure apart from each other so that they do not come into close contact with each other. Consequently, interference patterns are not produced, thus making it possible to maintain the quality of a visible image to be displayed on the liquid crystal display device at a high level.
(2) A second liquid crystal display device of the present invention comprises a liquid crystal structure having liquid crystal filled between a pair of substrates, a light source which emits light, a light-guiding member, disposed at the observer side of the liquid crystal structure, for guiding the light from the light source to the liquid crystal structure, and a cover disposed at the observer side of the light-guiding member, wherein a spacer member is disposed between the light-guiding member and the cover at peripheral portions of the light-guiding member and the cover so as to be in close contact with the light-guiding member and the cover.
The liquid crystal display device differs from the liquid crystal display device of Section (1) in that (1) a cover is disposed at the observer side of a light-guiding member, and (2) a spacer member is disposed between a light-conducting member and a cover. The cover primarily protects the liquid crystal member and the liquid crystal structure.
In the liquid crystal display device, a spacer member is disposed between a light-guiding member and a cover at the peripheral portions thereof so as to be in close contact therewith, so that dust no longer enters between the light-guiding member and the cover, as a result of which the quality of a visible image to be displayed on the liquid crystal display device can be maintained at a high level. In addition, the spacer member keeps the light-guiding member and the spacer apart from each other so that they do not come into close contact with each other. Consequently, interference patterns are not produced, thus making it possible to maintain the quality of a visible image to be displayed on the liquid crystal display device at a high level.
(3) A third liquid crystal display device according to the present invention comprises a liquid crystal structure having liquid crystal filled between a pair of substrates, a light source which emits light, a light-guiding member, disposed at the observer side of the liquid crystal structure, for guiding the light from the light source to the liquid crystal structure, and a cover disposed at the observer side of the light-guiding member, wherein the liquid crystal display device further comprises a first spacer member disposed between the light-guiding member and the liquid crystal structure at the peripheral portions of the light-guiding member and the liquid crystal structure so as to be in close contact with the light-guiding member and the liquid crystal structure, and a second spacer member disposed between the light-guiding member and the cover at the peripheral portions of the light-guiding member and the cover so as to be in close contact with the light-guiding member and the cover.
The liquid crystal display device differs from the liquid crystal display devices of Sections (1) and (2) in that spacer members are provided between the light-guiding member and the liquid crystal structure as well as between the light-guiding member and the cover. By virtue of this structure, it is possible to prevent entry of dust between the liquid crystal structure and the light-guiding member and between the light-guiding member and the cover, and to eliminate the problem of non-uniform close contact between the liquid crystal structure and the light-guiding member and between the light-guiding member and the cover, so that interference patterns of light are not produced.
(4) In the liquid crystal display devices of Sections (1) or (2), it is preferable that the spacer member be provided in at least 80% of the entire peripheral portions associated thereto. In FIG. 4, the spacer member is provided in 100% of an annular peripheral portion P of the light-guiding member 3. In FIG. 5, the spacer member is shown as being provided in at least 80% of the entire peripheral portion P of the light-guiding member 3. In this case, gaps K are formed in the spacer member in the peripheral portion P such that the portions of the spacer member remaining after the formation of these gaps K occupy at least 80% of the peripheral portion P of the light-guiding member 3. These gaps K may be formed in any location of the peripheral portion P.
The occupying area of the spacer member is set to at least 80%, based on experiments carried out by the present inventor et al. This is because when the occupying area of the spacer member is less than 80% dust enters the liquid crystal display device and reduces the display quality of the liquid crystal display device, whereas when the occupying area of the spacer member is at least 80% the amount of dust entering the liquid crystal display device can be reduced to an amount that does not, in practice, affect the display quality of the liquid crystal display device.
(5) In the liquid crystal display device of Section (3), it is preferable that the first spacer member and/or the second spacer member be provided in at least 80% of the entire peripheral portions associated thereto. The meaning of xe2x80x9cbeing provided in at least 80% of the entire peripheral portionsxe2x80x9d and the reason for setting the critical values of the occupying area of the spacer member or the spacer members at 80% are as described in Section (4).
(6) In the liquid crystal display devices of Sections (1) or (2), the spacer member may be formed in an endless annular form over the entire peripheral portions associated thereto.
(7) In the liquid crystal display device of Section (3), the first spacer member and/or the second spacer member is formed in an endless annular form over the entire peripheral portions associated thereto. This can virtually completely prevent the entry of dust.
(Electronic Device)
The electronic device of the present invention is one employing any one of the liquid crystal display devices of Sections (1) to (7) as a visible image display portion. Examples thereof include a portable telephone and a portable information terminal. According to the electronic device of the present invention, the liquid crystal display device used as visible image display portion in the electronic device can prevent dust from entering between the liquid crystal member and the liquid crystal structure or between the light-guiding member and the cover, and can prevent the production of interference patterns of light by forming a gap between the liquid crystal member and the liquid crystal structure and between the light-guiding member and the cover.